Engineering - Materials Selection in Mechanical Design Part 14 pdf

Case studies: use of data sources 14.1 Introduction and synopsis Screening requires data sources with one structure, further information, sources with another. This chapter illustrates what they look like, what they can do and what they cannot. The procedure follows the flow-chart of Figure 13.2, exploring the use of handbooks, databases, trade-association publications, suppliers data sheets, the Internet, and, if need be, in-house tests. Examples of the use of all of these appear in the case studies which follow. In each we seek detailed data for one of the materials short-listed in various of the case studies of earlier chapters. Not all the steps are reproduced, but the key design data and some indication of the level of detail, reliability and difficulty are given. They include examples of the output of software data sources, of suppliers data sheets and of information retrieved from the World-wide Web. Data retrieval sounds a tedious task, but when there is a goal in mind it can be fun, a sort of detective game. The problems in Appendix B at the end of this book suggests some to try. 14.2 Data for a ferrous alloy - type 302 stainless steel An easy one first: finding data for a standard steel. A spring is required to give a closing torque for the door of a dishwasher. The spring is exposed to hot, aerated water which may contain food acids, alkalis and salts. The performance indices for materials for springs MI = 6 - E M2 = ~ 4 (small springs) or (cheap springs) ECR, a2 -1- E MI = (small springs) or 0-" f M2 = :Ec; (cheap springs) A screening exercise using the appropriate charts, detailed in Case Study 6.8, led to a shortlist which included elastomers, polymers, composites and metals. Elastomers and polymers are elimi- nated here by the additional constraint on temperature. Although composites remain a possibility, the obvious candidates are metals. Steels make good springs, but ordinary carbon steels would corrode in the hot, wet, chemically aggressive environment. Screening shows that stainless steels can tolerate this. The detailed design of the spring requires data for the properties that enter M lor M 2, -the strength at (in the case of a metal, the yield strength ay), the modulus E, the density p and the cost C m -and data for the resistance to corrosion. The handbooks are the place to start. Case studies: use of data sources 335 Table 14.1 Data for hard drawn type 302 stainless steels* Property Density (Mg/m3) Modulus E (GPa) 0.2% Strength oy (MPa) Tensile strength (MPa) Elongation (%) Corrosion resistance cost Source A* Source B* Source C’ 7.8 210 965 1280 9 ‘Good’ No information 7.9 215 1000 1466 6 ‘Highly resistant’ No information 7.86 193 1345 - - No information No information ~~~ *Source A: ASMMerals Handbook, 10th Edition, Vol. 1 (1990); Source B: Smithells (1987); Source C: http.//www.matweb.com. All data have been converted to SI units. Source A, the ASM Metals Handbook and Source B Smithells (1987) both have substantial entries listing the properties of some 15 stainless steels. Hard-drawn Type 302 has a particularly high yield strength, promising attractive values of the indices M1 and M2. Information for Type 302 is abstracted in Table 14.1. Both handbooks give further information on composition, heat treatment and applications. The ASM Metals Handbook adds the helpful news: ‘Type 302 has excellent spring properties in the fully hard or spring-temper condition, and is readily available’. The World-wide Web yields Source C, broadly confirming what we already know. No problems here: the mechanical-property data from three quite different sources are in substan- tial agreement; the discrepancies are of order 2% in density and modulus, and 10% in strength, reflecting the permitted latitude in specification on composition and treatment. To do better than this you have to go to suppliers data sheets. One piece of information is missing: cost. Handbooks are reluctant to list it because, unlike properties, it varies. But a rough idea of cost would be a help. We turn to the databases. MatDB is hopelessly cumbersome and gives no help. The CMS gives the property profile shown in Figure 14.1; it includes the information: ‘Price: Range 1.4 to 1.6 Ekg’ (or 1.1 to 1.3 $Ab). Not very precise, but enough to be going on with. Postscript We are dealing here with a well-bred material with a full pedigree. Unearthing information about it is straightforward. That given above is probably sufficient for the dishwasher design. If more is wanted it must be sought from the steel company or the local supplier of the material itself, who will advise on current availability and price. Related case studies Case Study 6.9: Materials for springs 14.3 Data for a non-ferrous alloy - AI-Si die-casting alloys Candidate materials determined in Case Study 6.6 for the fan included aluminium alloys. Processing charts (Chapter 12) establish that the fan could be made with adequate precision and smoothness by die casting. To proceed with detailed design we now need data for density, p, and strength af; 336 Materials Selection in Mechanical Design Name: Wrought austenitic stainless steel, AIS1 302 State: HT grade D Composition Fek. ISC/17-19Cr/S-I INi/<2Mn/< ISi/<.045P/i.O3S Similar Standards UK (BS): 302825: UK (former BS): En 58A; ISO: 683NII1 Type 12; USA (UNS): S30200; Germany (W Nr.): 1.4300; Germany (DIN): XI2 CrNi 18 8; France (AFNOR): 212 CN 18.10; ltaly (UNI): XI5 CrNi 18 09; Sweden (SIS): 2332; Japan (JIS): SUS 302: Genera I Densitq Price Mechanical Bulk Modulus Compressive Strength Ductility Elastic Limit Endurance Limit Fracture Toughness Hardness Loss Coefficient Modulus of Rupture Poisson’s Ratio Shear Modulus Tensile Strength Young’s Modulus Thermal Latent Heat of Fusion Maximum Service Temperature Melting Point Minimum Service Temperature Specific Heat Thermal Conductivity Thermal Expansion Electrical Resistivity 7.81 1.75 134 760 0.05 760 436 68 3.50E+3 2.90E-4 760 0.265 74 1.03E+3 189 260 I .02E+3 1.67E+3 I 490 15 16 65 8.01 2.55 146 900 0.2 900 753 185 5.70E+3 4.80E-4 900 0.275 78 2.24E+3 197 285 I .20E+3 1.69E+3 2 530 17 20 77 Mg/m3 Ekg GPa MPa MPa MPa MPa ml/’ MPa MPa GPa MPa GPa kJkg K K K Jkg K W/m K 1 0-6/K lo-* ohm m Typical uses Exhaust parts; internal building fasteners; sinks; trim; washing-machine tubs; water tubing, springs References Elliot, D. and Tupholrne, S.M. ‘An Introduction to Steel, Selection: Part 2, Stainless Steels’, OUP (1981); ‘Iron & Steel Specifications’, 8th edition (1995), BISPA, 5 Cromwell Road, London, SW7 2HX; Brandes, EA. and Brook, G.R. (eds.) ‘Smithells Metals Reference Book’ 7th Edition (1992), Buttenvorth- Heinernann, Oxford, UK. ASM Metals Handbook (9th edition), Vol. 3, ASM International, Metals Park, Ohio, USA (1980); ’Design Guidelines for the Selection and Use of Stainless Steel’, Designers’ Handbook Series no.9014, Nickel Development Institute (1991); Fig. 14.1 Part of the output of the PC-format database CMS for Type 302 stainless steel. Details of this and other databases are given in the Appendix to Chapter 13, Section 13A.5. Case studies: use of data sources 337 in this case we might interpret af as the fatigue strength. Prudence suggests that we should check the yield and ultimate strengths too. Aluminium alloys, like steels, have a respectable genealogy. Finding data for them should not be difficult. It isn't. But there is a problem: a lack of harmony in specification. We reach for the handbooks again, Volume 2 of the ASM Metals Handbook reveals that 85% of all aluminium die- castings are made of Alloy 380, a highly fluid (i.e. castable) alloy containing 8% silicon with a little iron and copper. It gives the data listed under Source A in Table 14.2. So far so good. But when we turn to Smithells (1987) we find no mention of Alloy 380, or of any other with the same composition. Among die-casting alloys, Alloy LM6 (alias 3L33 and LM20) features. It contains 11.5% silicon, and, not surprisingly, has properties which differ from those of Alloy 380. They are listed under Source B in Table 14.2. The density and modulus of the two alloys are the same, but the fatigue strength of LM6 is le$s than half that of Alloy 380. This leaves us vaguely discomforted. Are they really so different? Are the data to be trusted at all? Before investing time and money in detailed design, we need corroboration of the data. A third handbook - the Chapman and Hall Materials Selector - gives data for LM6 (Source C, Table 14.2); it fully corroborates Smithells. This looks better, but just to be sure we seek help from the Trade Federations: the Aluminium Association in the US; the Aluminium Federation (ALFED) in the UK. We are at this moment in the UK - we contact ALFED - they mail their publication The Properties of Aluminium and its Alloys. It contains everything we need for LM6, including its seven equivalent names in Europe, Russia and Australasia. The data for moduli and strength are identical with those of Source C in the Table - Mr Chapman and Ms Hall got their data from ALFED, a sensible thing to have done. A similar appeal to the US Aluminium Association reveals a similar story - their publication was the origin of the ASM data of Source A. So there is nothing wrong with the data. It is just that die-casters in the US use one alloy; those in Europe prefer another. But what about cost? None of the handbooks help. A quick scan through the WWW sites listed in Chapter 13 directs us to the London Metal Exchange http://www.metalprice.com./. Todays quoted price for aluminium alloy is AI-alloy 1.408 to 1.43 $/kg. Postscript Discord in standards is a common problem. Committees charged with the task of harmonization sit late into the EU night, and move slowly towards a unifying system. In the case of both steels and aluminium alloys, the US system of specification, which has some reason and logic to it, is likely to become the basis of the standard. Table 14.2 Data for aluminium alloys 380 and LM6 Property Source A* Source B* Source c* ~~~~~~ ~~ ~ ~ ~- Density (Mg/m3) 2.7 2.65 2.65 0.2% Yield strength (MPa) 165 17 80 Fatigue strength (MPa) 145 62 68 Modulus (GPa) 71 70.6 71 Ultimate strength (MPa) 330 216 200 Elongation (%) 3 10 13 'Source A: ASM Metals Handbook, 10th Edition, Volume 2 (1990); Source B: Smithells (1 987); Source C: Chapman and Hall Mulerials Selector (1 997) and ALFED (1981). All data have been convened to SI units. 338 Materials Selection in Mechanical Design Related case studies Case Study 6.7: Case Study 12.2: Forming a fan Case Study 12.6: Economical casting Materials for high-flow fans 14.4 Data for a polymer - polyethylene Now something slightly less clear cut: the selection of a polymer for the elastic seal analysed in Case Study 6.10. One candidate was low-density polyethylene (LDPE). The performance index required data for modulus and for strength; we might reasonably ask, additionally, for density, thermal properties, corrosion resistance and cost. Start, as before, with the handbooks. The Chapman und Hall Materials Selector compares various grades of polyethylene; its data for LDPE are listed in Table 14.3 under Source A. The Engineered Materials Handbook, Vol. 2, Plastics, leaves us disappointed. The Polymers for Engineering Appli- cations (1987) is rather more helpful, but gives values for strength and thermal properties which differ by a factor of 2 from those of Source A, and no data at all for the modulus. The Handbook of Polymers and Elastomers (1 979, after some hunting, gives the data listed under Source B - big discrepancies again. The Materials Engineering 'Materials Selector' (Source C) does much the same. None give cost. Things are not wholly satisfactory: we could do this well by simply reading data off the charts of Chapter 4. We need something better. How about computer databases? The PLASCAMS and the CMS systems both prove helpful. We load PLASCAMS. Some 10 keystrokes and two minutes later, we have the data shown in Figure 14.2. They include a modulus, a strength, cost, processing information and applications: we are reassured to observe that these include gaskets and seals. The same database also contains the address and phone number of suppliers who will, on request, send data sheets. All much more satisfactory. Table 14.3 Data for low-density polyethylene (LDPE) Property Source A* Source B* Source C Density (Mg/m3) 0.92 Modulus (CPa) 0.25 Heat deflection temp ("C) 50 Max service temp ("C) 50 T-expansion ( lop6 K-') 200 T-conductivity (W/m K) - Tensile strength (MPa) 9 Rockwell hardness D48 Corrosion in wateddilute acid satisfactory 0.91 -0.93 0.1 -0.2 43 82 100 - 200 0.33 4-15 D41-50 resistant 0.92 0.2 69 0.33 13 D50 ex c e 11 en t - 160-198 *Source A: Chapman and Hall Materials Selector (1997); Source B: Handbook of Polymers and Elastomers (1975); Source C: Materials Engineering Materials Selector (1997). All data have been converted to SI units. Case studies: use of data sources 339 Material: 119 LDPE Resin type: TP S.Cryst. Costltonne: 600 S.G. 0.92 Max. Operating Temp Water absorption Tensile strength Flexural modulus Elongation at break Notched Izod HDT @ 0.45 MPa HDT @ 1.80 MPa Matl. drying Mould shrinkage "C % MPa GPa % kUm "C "C hrs @ ' 8 50 0.01 IO 0.25 40 1.06+ 50 35 'C NA 3 Surface hardness Linear expansion Flammability Oxygen index Vol. Resist. Dielect. strength Dielect. const. lkHz Dissipation Fact. lkHz Melt temp. range Mould temp. range SD48 E-5 20 UL94 HB % 17 log Qcm 16 MVIm 27 2.3 0.0003 "C 220-260 "C 20-40 ADVANTAGES properties. DISADVANTAGES APPLICATIONS squeeze bottles. Heat-seal film for metal laminates. Pipe, cable covering, core in UHF cables. Cheap, good chemical resistance. High impact strength at low temperatures. Excellent electrical Low strength and stiffness. Susceptible to stress cracking. Flammable. Chemically resistant fittings, bowls, lids, gaskets, toys, containers packaging film, film liners, Fig. 14.2 Part of the output of PLASCAMS, a PC database for engineering polymers, for low-density polyethylene. It also gives trade names and addresses of UK suppliers. Details of this and other databases are given in the Appendix to Chapter 13, Section 13A.5. But is it up to date? Not, perhaps, as much so as the World-wide Web. A search reveals company-specific web sites of polymer manufacturers (GE, Hoechst, ICI, Bayer and more). It also guides us to sites which collect and compile data from suppliers data sheets. One such is http://www.matweb.com./ from which Figure 14.3 was downloaded. Postscript There are two messages here. The first concerns the properties of polymers: they vary from supplier to supplier much more than do the properties of metals. And the way they are reported is quirky: a flexural modulus but no Young's modulus; a Notched Izod number instead of a fracture toughness, and so on. These we have to live with for the moment. The second concerns the relative ease of use of handbooks and databases: when the software contains the information you need, it surpasses, in ease, speed and convenience, any handbook. But software, like a book, has a publication date. The day after it is published it is, strictly speaking, out of date. The World-wide Web is dynamic; a well maintained site yields data which has not aged. Related case studies Case Study 6.10: Elastic hinges Case Study 6.11: Materials for seals 340 Materials Selection in Mechanical Design Polyethylene, Low Density; Molded/Extruded Polymer properties are subject to a wide variation. depending on the grade specified Physical Properties Density. gicc Linear Mold Shrinkage, cm/cm Water Absorption, % Hardness, Shore D Mechanical Properties Tensile Strength, Yield, MPa Tensile Strength, Ultimate, MPa Elongation 5%; break Modulus of Elasticity, GPa Flexural Modulus, GPa lzod lmpact in J. J/cm, or J/cm' Thermal Properties CTE, linear 20"C, pm/m-"C HDT at 0.46 MPa, "C Processing Temperature, "C Melting Point, "C Maximum Service Temp, Air, "C Heat Capacity, J/g-"C Thermal Conductivity. W/m-K Electrical Properties Electrical Resistivity, Ohm-cm Dielectric Constant Dielectric Constant, Low Frequency Dielectric Strength, kV/mm Dissipation Factor Dissipation Factor, Low Frequency Values 0.9 I 0.03 1 .5 44 Values 10 25 400 0.2 0.4 999 Values 30 45 200 115 70 2.2 0.3 Values 1E+16 2.3 2.3 19 0.0005 0.0005 Comments 0.910-0.925 g/Cc 1.5-5% ASTM D955 in 24 hours per ASTM D570 41 -46 Shore D Comments 4- 16 MPa; ASTM D638 7-40 MPa 0.07-0.3 GPa; In Tension; ASTM D638 0-0.7 GPa; ASTM D790 No Break; Notched 100-800%; ASTM D638 Comments 20-40 pm/m-"C; ASTM D696 150-320°C 60-90°C~ 2.0-2.4 J/g-"C; ASTM C351 ASTM C177 40-50°C Comments ASTM D257 2.2-2.4; 50-100 Hz; ASTM D150 18-20 kV/mm; ASTM D149 Upper Limit; 50-100 Ha; ASTM D150 Upper Limit; 50-100 Hz; ASTM D150 2.2-2.4; 50-100 Hz; ASTM D150 Fig. 14.3 Data for low-density polyethylene from the web site http://www.matweb.com. 14.5 Data for a ceramic - zirconia Now a challenge: data for a novel ceramic. The ceramic valve of the tap examined in Case Study 6.20 failed, it was surmised, because of thermal shock. The problem could be overcome by choosing a ceramic with a greater thermal shock resistance. Zirconia (ZrO2) emerged as a possibility. The performance index ut M=- Ea contains the tensile strength, a,, the modulus E and the thermal expansion coefficient a. The design will require data for these, together with hardness or wear resistance, fracture toughness, and some indication of availability and cost. Case studies: use of data sources 341 Table 14.4 Data for zirconia Properties Source A* Source B* Source C* Source D* Source E* Density (Mg/m’) 5 .O- 5.8 5.4 - 6.0 5.65 Tensile strength (MPa) 240 - Modulus of rupture (MPa) 83 400-800 550 Fracture toughness (MPa m’”) 2.5 -5 7.6 4.7 4.5 8.4 T-conductivity (Wlm K) 1.8 2.4 1.8 1.7-2.0 1.67 *Source A: Morrell, Handbook of Properties of Techrzical and Engineering Ceramics (1985); Source B: ASM Engineered Materials Reference Book (1989); Source C: Handbook of Ceramics and Composites (1990); Source D: Chapman and Hall ‘Muterials Selector’ (1997): Source E: http.//matweb.com./. All data have been converted to SI units. Modulus (GPa) 200 I50 150 200 200 - - - - - Hardness (MPa) 12 000 11 000 6000 12 000 11 000 T-expansion (1 O-‘ K-’ ) 8-9 4.9 7 8-9 7 After some hunting, entries are found in four of the handbooks; the best they can offer is listed in Table 14.4. One (the ASM Engineered Materials Reference Book), supplies the further information that zirconia ‘has low friction coefficient, good wear and corrosion resistance, good thermal shock resistance, and high fracture toughness’. Sounds promising; but the numeric data show alarming divergence and have unpleasant gaps. No cost data, of course. There are large discrepancies here. It is not unusual to find that samples of ceramics which are chemically identical can be as strong as steel or as brittle as a biscuit. Ceramics are not yet manufactured to the tight standards of metallic alloys. The properties of a zirconia from one supplier can differ, sometimes dramatically, from those of material from another. But the problem with Source B, at least, is worse: a modulus of rupture (MOR) of 83MPa is not consistent with a tensile strength of 240MPa; as a general rule, the MOR is greater than the tensile strength. The discrepancy is too great to be correct; the data must either have come from two quite different materials or be just plain wrong. All this is normal; one must expect it in materials which are still under development. It does not mean that zirconia is a bad choice for the valve. It means, rather, that we must identify suppliers and base the design on the properties they provide. Figure 14.4 shows what we get: supplier’s data for the zirconia with the tradename AmZirOx. Odd mixture of units, but the conversion factors inside the covers of this book allow them to be restored to a consistent set. The supplier can give guidance on supply and cost (zirconia currently costs about three times more than alumina), and can be held responsible for errors in data. The design can proceed. Postscript The new ceramics offer design opportunities, but they can only be grasped if the designer has confidence that the material has a consistent quality, and properties with values that can be trusted. The handbooks and databases do their best, but they are, inevitably, describing average or ‘typical’ behaviour. The extremes can lie far from the average. Here is a case in which it is best, right from the start, to go to the supplier for help. Related case studies Case Study 6.21 : Ceramic valves for taps Case Study 12.5: Forming a ceramic tap valve 342 Materials Selection in Mechanical Design TECHNICAL DATA AmZirOX (Astro Met Zirconium Oxide) is a yttria partially stabilized zirconia advanced ceramic material which features high strength and toughness making it a candidate material for use in severe structural applications which exhibit wear, corrosion abrasion and impact. AmZirOX has been developed with a unique microstructure utilizing transformation toughening which allows AmZirOX to absorb the energy of impacts that would cause most ceramics to shatter. AmZirOX components can be fabricated into a wide range of precision shapes and sizes utilizing conventional ceramic processing technology and finishing techniques. PROPERTIES UNITS VALUE Color Density Water Absorption Gas Permeation Hardness Flexural Strength Modulus of Elasticity Fracture Toughness Poisson’s Ratio - g/cm3 % % Vickers MPa (KPSI) GPa (lo6 psi) MPam‘I’ - Ivory 6.01 0 0 1250 1075 (156) 207 (30) 9 100 Thermal Expansion (25°C- 1000°C) 10@/”C (10@/”F) 10.3 (5.8) Thermal Conductivity Btu in/ft2h”F 15 Specific Heat caVC gm 0.32 Maximum Temperature Use (no load) “C (OF) 2400 (4350) Fig. 14.4 A supplier’s data sheet for a zirconia ceramic. The units can be converted to SI by using the conversion factors given inside the front and back covers of this book. 14.6 Data for a glass-filled polymer - nylon 30% glass The main bronze rudder-bearings of large ships (Case Study 6.21) can be replaced by nylon, or, better, by a glass-filled nylon. The replacement requires redesign, and redesign requires data. Stiff- ness, strength and fatigue resistance are obviously involved; friction coefficient, wear rate and stability in sea water are needed too. Start, as always, with the handbooks. Three yield information for 30% glass-filled Nylon 6/6. It is paraphrased in Table 14.5. The approach of the sources differs: two give a single ‘typical’ value for each property, and no information about friction, wear or corrosion. The third (Source C) gives a range of values, and encouragement, at least, that friction, wear and corrosion properties are adequate. The things to observe are, first, the consistency: the ranges of Source C contain the values of the other two. But - second - this range is so wide that it is not much help with detailed design. Something better is needed. The database PLASCAMS could certainly help here, but we have already seen what PLASCAMS can do (Figure 14.2). We turn instead to dataPLAS and find what we want: 30% glass-filled Nylon 6/6. Figure 14.5 shows part of the output. It contains further helpful comments and addresses for Case studies: use of data sources 343 POLYAMIDE 6.6 FERRO MECHANICAL PROPERTIES Unit Tensile Yield Strength Ultimate Tensile Strength Elongation at Yield Elongation at Break Tensile Modulus Flexural Strength Flexural Modulus Compressive Strength Shear Strength Izod Impact Unnotched, 23 '/2 C Izod Impact Unnotched, -40 '/2 C Izod Impact Notched, 23 1/2 C Izod Impact Notched, -40 1/2 C Tensile Impact Unnotched, 23 '/2 C Rockwell hardness M Rockwell hardness R Shore hardness D Shore hardness A psiE3 psiE3 7c % psiE3 psiE3 psiE3 psiE3 psiE3 FLbh FLb/in FLb/in FLbIin FLP/i2 - - - - THERMAL PROPERTIES Unit DTUL @ 264 psi (1.80 MPa) DTUL @ 66 psi (0.45 MPa) Vicat B Temperature, 5 kg Vicat A Temperature, 1 kg Continuous Service Temperature Melting Temperature Glass Transition Thermal Conductivity Brittle Temperature Linear Thermal Expansion Coeff "F "F "F "F "F "F "F W/m K -OF E-5F Value - 19.7 2.8 942 26.8 812 23 11 7 6 1.4 0.7 90 115 85 - - - Value 40 1 428 410 284 424 0.35 1.67 - - - Fig. 14.5 Part of the output of dataPLAS, a PC database for US engineering polymers, for 30% glass-filled Nylon 6/6. Details of this and other databases are given in the Appendix to Chapter 13, Section 13A.5. suppliers (not shown), from whom data sheets and cost information, which we shall obviously need, can be obtained. Postscript Glass-filled polymers are classified as plastics, not as the composites they really are. Fillers are added to increase stiffness and abrasion resistance, and sometimes to reduce cost. Data for filled polymers can be found in all the handbooks and databases that include data for polymers. Related case studies Case Study 6.22: Bearings for ships' rudders [...]... Price ($/kg) K-') T-expansion ( T-conductivity (W/m K) Specific heat ( J k g K ) Modulus (GPa) Yield strength (MPa) Ultimate strength (MPa) Ductility (%) Source A* 2.91 - 14. 4 125 800 121 44 1 593 4.5 Source B* 2.9 - 13.5 - 125 430 610 5.0 Source C" 2. 9-2 .95 10 0-1 70 12. 4- 13.5 12 3-1 28 80 0-8 40 12 1-1 2s 43 0-4 45 59 0-6 10 4. 0-6 .0 "Source A: Engineers Guide m Composite Materials (1987) reporting data from... comment No comment 20 - 165 3 -4 107 0.49 - 2. 5-3 .4 1 5-5 0 0.21 -0 .48 Uses include: unlubricated gears, bearings and antifriction parts Good in water *Source A: Reinforced Plastics: Properties and Applications (1991); Source B: Engineers Guide to Composite Materials (1987); Source C : ASM Engineered Materials Handbook, Vol 2 (1989) 14. 7 Data for a metal-matrix composite (MMC) - Ai/SiC, An astronomical... can be laid-up in thousands of ways It 346 Materials Selection in Mechanical Design Table 14. 7 Data for 0/90/f45 carbon in epoxy Properties Density (Mg/m3) Modulus (GPa) Tensile strength (MPa) Compressive strength (MPa) T-expansion ( K-’) T-conductivity (W/m K) Source A* 1.54 65 503 503 Source B* 1.55 72 550 400 - - - 8 Source C* 1.55 60 700 - 20 5 *Source A: ASM Engineers Guide to Composite Materials. ..344 Materials Selection in Mechanical Design Table 14. 5 Data for nylon 6/6, 30% glass filled Proper@ Source A” Source B* Source C* 1.37 1.3 1. 3- 1.34 265 260 260 12 0-2 50 - 9 9 I80 180 3 186 10 0- 193 16 5-2 76 Density (Mg/m3) Melting point (“C) Heat deflection temp (“C) Tensile modulus (GPa) Tensile strength (MPa) Compressive strength (MPa) Elongation (5%) T-expansion ( K-’) T-conductivity (W/m... the grain; i means perpendicular 348 Materials Selection in Mechanical Design Name Common Name Ochroma spp (MD), parallel to grain Balsa (MD)L General Properties Density Diff Shrinkage (Rad.) Diff Shrinkage (Tan.) Rad Shrinkage (green to oven-dry) Tan Shrinkage (green to oven-dry) Vol Shrinkage (green to oven-dry) 0.17 0.05 0.07 3.2 3.5 6 0.21 0.06 0.09 7 5.3 9 Mglm' 9% per % MC % per % MC Mechanical. .. Woods, generally, are used in low-performance applications (building, packaging) where safety margins are large; then a little uncertainty in properties does not matter But there are other examples: balsa and spruce in aircraft; ash in automobile frames, vaulting poles, oars, yew in bows, hickory in skis, and so on Then attention to these details is important Postscript All natural materials have the difficulties... Laminate theory allows the stiffness and strength of a given lay-up to be computed when the properties of fibres and matrix are known Designers in large industries use laminate theory to decide on number and lay-up of plies, but few small industries have the resources to do this The second is experimental: a trial lay-up is tested, measuring the responses which are critical to the design, and the lay-up... Accepting or rejecting them becomes an additional design decision Related case studies Case Study 6.3: Mirrors for large telescopes Case Study 6.20: Materials to minimize thermal distortion in precision devices 14. 8 Data for a polymer-matrix composite - CFRP If a design calls for a material which is light, stiff and strong (Case Studies 6.2, 6.3, 6.5 and 6.8), it is likely that carbon-fibre reinforced... before 1986 will not help much here - most of the development has occurred since then We turn to the Engineers Guide to Composite Materials (1987) and find limited data, part of it derived from a material of one producer, the rest from that of another (Table 14. 6, Source A), leaving us uneasy about consistency This is a bit thin for something to be shot into space Minor miscalculations here become major... simple metals, for which welltried testing and documentation procedures exist Because they are metals, their properties are measured and recorded in well-accepted ways Lack of standards, inevitable at this stage, creates problems Further into the future lie ceramic-matrix composites They exist, but cannot yet be thought of as engineering materials For fibre-reinforced polymers, the picture is different . 6.9: Materials for springs 14. 3 Data for a non-ferrous alloy - AI-Si die-casting alloys Candidate materials determined in Case Study 6.6 for the fan included aluminium alloys. Processing. 2. 9-2 .95 Price ($/kg) - - 10 0-1 70 Specific heat (JkgK) 800 - 80 0-8 40 Modulus (GPa) 121 125 121 -1 2s T-expansion ( K-') 14. 4 13.5 12. 4- 13.5 T-conductivity (W/m K) 125 -. I50 150 200 200 - - - - - Hardness (MPa) 12 000 11 000 6000 12 000 11 000 T-expansion (1 O-‘ K-’ ) 8-9 4.9 7 8-9 7 After some hunting, entries are found in four of the handbooks;